Understanding Graphs
A graph is a diagram that shows the relationship between two or more things. Below are shown a
graph and its components.
Title – tells us what the graph is about.
Labels – tells us what types of facts are contained on the graph.
Scales – shows us how much or how many.
Points – shows us the facts.
Lines – shows us an estimate for the values between the points.
The horizontal axis, which sometimes is referred to as the x axis, is normally used to represent the
independent variable. The independent variable determines the value of the other variables. The
vertical axis, which sometimes is referred to as the y axis, is normally used to represent the dependent
variable. The dependent variable value is determined by the value of the independent variable. For
example, in the equation for the area of a circle, A=πr2, the radius (r) is the independent variable and the
area (A) is the dependent variable. So, if we measured the radius of several circles, calculated their
areas, and graphed this information, then the value for the radius would be on the horizontal axis and
the value for the area would be on the vertical axis. By connecting these points with a line, we would be
able to use the graph to determine the area of a circle whose radius we did not measure.
You are able to answer questions based upon the information within a graph. See example below.
QUESTION
ANSWER
1. What is the title of this line graph?
Temperatures in New York City
2. What is the range of values on the horizontal scale?
1 to 6
3. What is the range of values on the vertical scale?
0 to 80
4. How many points are in the graph?
6
5. What was the lowest temperature recorded?
43° F
6. What was the highest temperature recorded?
67° F
7. At what point did the temperature dip?
Day 3: 50° F
Graphs related to chemistry
This graph shows the relationship between temperature in degrees Fahrenheit and degrees Celsius. You
can determine the temperature in Fahrenheit if you know the temperature in Celsius. For example, if
the temperature is 80⁰C, then you follow the dashed line up until it intersects with the blue line. Next
you draw a horizontal line from where the dashed line intersected the blue line to the vertical axis. This
horizontal line intersects the vertical axis at about 175. So, when the temperature is 80⁰C, then the
temperature is about 175⁰F. You can go through a similar process if you know the temperature in
degrees Fahrenheit and want to find the temperature in degrees Celsius.
This graph shows the relationship between the absorbance of light and the concentration of a solution.
This graph can be used to determine the concentration of a solution by measuring its absorbance. For
example, if you measure the absorbance of a solution as 0.6, then by drawing lines, as in the above
temperature graph, you can determine the concentration of your solution to be about 65%. You will be
doing a similar experiment, except instead of measuring the absorbance; you will be measuring the
density. Then based upon the graph that you draw, you will determine the concentration of an
unknown solution.
This graph shows the change in energy as a reaction takes place. It is called an Energy of Activation
diagram. The vertical axis shows the amount of energy, while the horizontal axis shows the progress of
the reaction from reactants to products. This graph shows that in order for a reaction to occur energy
must be added (energy value increases as move towards high point). Once the reaction has taken place
the energy decreases (energy value decreases from high point towards product) with the product being
at lower energy than the reactants. This diagram also shows that the use of an enzyme decreases the
amount of energy needed for the reaction to take place, which makes the reaction more efficient. The
chemical reaction shown is one of the reactions that occurs within you to maintain the pH within your
blood and cells.